Many industries require detailed tracing of critical inventoried items from a manufacturer to an end user. Of particular interest is the FAA mandated tracing and certification of flight safety critical aircraft components used both in original equipment manufacture and as repair parts. Replacement parts may pass through a number of hands and spend an unpredictable amount of time in inventory before being used. The multiplicity of flow paths and the potentially long delay between manufacture and use offers an opportunity for surreptitious substitution of inferior, lower-cost parts--a practice that has led to fatal aircraft crashes. There is a need for a reliable and secure system of tracking aircraft parts from their point of manufacture to their point of ultimate use.
The art of electronic article surveillance (EAS) tagging provides useful technical information on the use of small, low-cost tags that can be attached to an article and that can be interrogated electronically. EAS tags are most commonly used for reducing theft from retail establishments by setting off an alarm whenever a tagged article is removed from a controlled area. Notable among this art are:
U.S. Pat. No. 5,168,263 to Drucker et al, who teach the use of a "smart tag" containing a tag microprocessor that communicates with other security apparatus via a radio-frequency link; and
U.S. Pat. No. 5,151,684 to Johnsen, who teaches a tag that sounds an alarm if the tag is removed from a protected article or if the article is removed from the protected store. Johnsen's tag communicates with other equipment to receive a signal indicating that the article has been sold, and disables its alarm in response to the "sold" message.
The EAS art includes a variety of methods of dealing with thieves who might try either to remove a tag prior to stealing merchandise or to shield the tag on an article of merchandise from detection apparatus located at the exit to a store. The tag art does not extend to providing countermeasures against sophisticated theft attempts involving communicating with a "smart tag" in order to defeat the security system by altering identification records or other data stored in the tag.
Other sorts of "smart tags", "smart tracers" or small datalogging devices are known for use in monitoring the operation of a piece of machinery or for following the progress of a complex item of equipment through a multi-step manufacturing process. Notable among the prior art in this area are:
U.S. Pat. No. 5,113,344 to Kellogg et al., who teach the use of a tag providing both datalogging and control functions for a materials handling vehicle. Kellogg et al.'s tag employs a non-volatile computer memory segmented into a read-only portion (which contains vehicle-specific operational limit data used by a general-purpose on-board vehicle controller to control vehicle speed, etc.) and a read/write portion (which may be used for maintenance-related operational data). Kellogg et al. use an EEPROM as their non-volatile memory device. This allows the device to be disconnected from electrical power for shipment and so that the vehicle to which it is attached can be maintained without loss of data.
U.S. Pat. No. 5,065,321 to Bezos et al, who teach the use of an on-board computer-based recorder to collect historical operational data and communicate these data, via an inductive coupling, to another portion of the measurement system.
Although a variety of measurements, data storage and retrieval methods have been provided by "smart tracer" datalogging devices, these devices are generally used in situations where data security is of little concern. This art area does not provide teaching of a data storage element resistant to sophisticated tampering.